This function is the only builtin with arrays as parameter.  A new
constexpr constructor is added to TType to support this, and
gen_builtin_symbols is changed to emit the correct type for offsets
parameter of this function.

Bug: angleproject:3569
Change-Id: I55af58b43f24cd605c622ee685b359535e11ef85
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1975431Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>